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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 720 (CRUISE CONTROL SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC P0568TEST DESCRIPTION
1999 GMC Forward Control 5.7 R, Automatic

Test Description

1999 GMC Forward Control 5.7 R, AutomaticSECTION Test Description
WARNING: This page is about a different car, the 2004 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.

The number below refers to the step number on the diagnostic table.

  1. 2:  This step determines if condition is present.
DTC P0568

Step Action Yes No
Schematic Reference: Cruise Control Schematics 
Connector End View Reference: Cruise Control Connector End Views  or Powertrain Control Module (PCM) Connector End Views in Engine Controls-5.7 L, or Throttle Actuator Control (TAC) Module Connector End Views in Engine Controls-5.7 L
1 Did you perform the Cruise Control Diagnostic System Check? Go to Step 2  Go to Diagnostic System Check - Cruise Control 
2 
  1. Install a scan tool.
  2. Turn the ignition ON, with the engine OFF.
  3. Turn the cruise On/Off control switch ON.
  4. With the scan tool, observe the Cruise Set/Coast Switch parameter in the PCM data list.
Does the Cruise Set/Coast Switch parameter display On?		 Go to Step 3  Go to Diagnostic Aids
3
  1. Turn the ignition OFF.
  2. Disconnect the cruise control switch.
  3. Turn the ignition ON, with the engine OFF.
  4. With the scan tool, observe the Cruise Set/Coast Switch parameter in the PCM data list.
Does the Cruise Set/Coast Switch parameter display On?		 Go to Step 4  Go to Step 5 
4 Test the cruise control set/coast switch signal circuit for a short to voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 9  Go to Step 6 
5 Inspect for poor connections at the harness connector of the cruise control switch. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 9  Go to Step 8 
6 Inspect for poor connections at the harness connector of the TAC module. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 9  Go to Step 7 
7 Replace the TAC module. Refer to Throttle Actuator Control (TAC) Module Replacement in Engine Controls-5.7 L.
Did you complete the replacement?		 Go to Step 9  -
8 Replace the cruise control switch. Refer to Multifunction, Turn Signal Switch Replacement in Steering Wheel and Column.
Did you complete the replacement?		 Go to Step 9  -
9
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC.
Does the DTC reset?		 Go to Step 2  System OK
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.